Aluminum complexes useful for cross-linking coating compositions

ABSTRACT

Aluminum complexes useful as cross-linking agents for coating compositions, especially high solids compositions containing an alkyd resin binder, are made by reacting a volatile oxime with a product of reaction of (1) an aluminum alcoholate or phenolate, (2) a carboxylic acid and/or β-diketo compound, and (3) optionally water.

This invention relates to aluminum complexes useful for cross-linkingcoating compositions, and more particularly to aluminum complexes whichare useful as driers and in some cases also rheology modifiers, incoating compositions of high solids content.

Conventional alkyd paint systems involve the use of substantial amountsof organic solvent, e.g. white spirit. To reduce the amount of solventrequired, coating compositions of high solids content have beendeveloped. Certain technical problems are involved. More particularly,conventional alkyd resins used in paints are of high molecular weightand only relatively few functional groups per molecule are required toform satisfactory cross-linked films. High solids content paint systems,on the other hand, require the use of lower molecular weight binders (sothat the composition shall have a sufficiently low viscosity for ease ofapplication), and for this reason a substantially larger number offunctional groups must be present per molecule so that the finalcross-linked film shall have the required high molecular weight.

Conventional alkyd paint films cross-link by reactions involvingoxidation and polymerization of the unsaturated alkyl groups present inthe drying oils used in making the alkyd resin. The drying processinvolves reaction of the film with atmospheric oxygen, and to promotethis reaction metallic soaps (driers) are incorporated in the paintcomposition. Cobalt and manganese soaps are effective at acceleratingthe surface drying of a paint film but are less effective in promotinguniform drying through the thickness of the coating. Lead driers arevery effective for promoting drying through the thickness of the film,but it is desirable to eliminate them from paint systems because of theinherent toxicity of lead. For this purpose, zirconium has been proposedas a replacement for lead because of its low toxicity. Zirconiumpromotes through drying of the paint film by coordination bonding.However, in high solids coatings, levels of cobalt, zirconium andcalcium driers which are satisfactory in conventional alkyd paintsystems are insufficiently effective to produce through drying.Consequently, to improve through drying, manufacturers of high solidscoating compositions have recommended increasing the zirconium levelfrom the standard level of about 0.09% up to 0.6% zirconium, and suchhigher levels of zirconium or other metal driers and other agents,especially chelating agents, are incorporated into alkyd resin basedcoating compositions of high solids content. The purpose of thechelating agents is to form soluble coordination complexes with thedrier metals and such complexes are generally found to be more effectiveas driers than uncomplexed metal salts. The usual chelating agentsincorporated in coating compositions for this purpose are1,10-phenanthroline and 2,2'-dipyridyl. However, in some cases even theuse of high levels of zirconium or other drier metals, with or without acomplexing agent, still does not produce adequate drying of the coatingcomposition. There is therefore a need for more effective drier systems.Moreover, the cost of using high levels of zirconium and chelating agentis itself a drawback in existing drier systems for compositions of highsolids content. Chelating agents may also give rise to discoloration ofthe paint film.

The rheology of coating compositions of high solids content also causesproblems. In a conventional alkyd based coating composition, when thesolvent evaporates, the alkyd resin left behind is very viscous and hasonly limited tendency to flow. However, with coating compositions ofhigh solids content, the resins left behind after evaporation of thesolvent are much less viscous and frequently flow in an undesirable wayto produce the problems of sagging and dripping. To reduce theseproblems, it is necessary to incorporate in the composition a rheologycontrol additive. An additive which promotes thixotropy in thecomposition reduces sagging and dripping, but thixotropic additives arefrequently ineffective in coating compositions of high solids contentand it is necessary to introduce into the composition a degree ofpseudoplasticity. High solids paint compositions formulated with apseudoplastic component can be made so that sagging and dripping areeliminated. However, a paint having a pseudoplastic rheology has otherundesirable properties. In particular, such paints are difficult andtiring to brush out because of the much higher viscous drag on the paintbrush. Also, pseudoplastic paints, unlike thixotropic paints, reformtheir structure immediately on brushing out so that brush marks areretained in the applied coating. It is therefore desirable to be able toproduce a high solids coating composition which becomes pseudoplasticonly after it has been applied. In this way, it would be possible toprovide a paint which would not exert undesirable viscous drag on thepaint brush or leave brush marks on application, but would neverthelessnot sag or drip after application.

Other metals have been proposed for use as driers in high solids coatingcompositions. For example, International specification WO91/15549proposes the use of neodymium carboxylates to improve through drying inhigh solids content coating compositions. It is stated that a level of0.1 to 0.4% neodymium combined with cobalt significantly improvesdrying, especially in thick films, when compared with zirconium,lanthanum or cerium even at high levels. This improvement is morepronounced when vanadium and potassium carboxylates and complexingagents such as 2,2'-dipyridyl are used. With a particular high solidsalkyd resin (Beckosol 10-539), a combination of cobalt, neodymium,vanadium, potassium and 2,2'-dipyridyl is recommended. However,neodymium is expensive and "loss of dry" (i.e. loss of drying capacityon storage) may be unsatisfactory with the combination of neodymium,cobalt, vanadium, potassium and 2,2'-dipyridyl proposed in thisspecification.

Coating compositions contain resins which have functional groups such ascarboxyl and hydroxyl groups, which have free electron pairs able toform coordinate linkages with metals such as zirconium; this coordinatebonding is an essential feature of the drying of the resin. It is knownthat aluminum compounds can form coordinate linkages with free electronpairs present in the resins used in surface coatings, and such compoundshave been proposed as replacements for lead and zirconium driers. Forexample, aluminum alkoxides, substituted alkoxides and polyoxo-aluminumcompounds as disclosed in British Specification No. 825878 and EuropeanPatent Specification 0018780 may be used. However, these aluminumcompounds are of only limited utility both in conventional an in highsolids alkyd resin-based coating compositions because aluminum has veryhigh affinity for the free carboxyl, hydroxyl and other groups in theresins capable of forming coordinate or covalent linkages. While thisaffinity is desirable in drying, it is undesirable while the coatingcomposition is being stored and frequently causes gelling of thecomposition which renders it unusable. The polyoxo aluminum compoundsdisclosed in European Specification 0018780 have a reduced tendency toform such gels, especially with resins which contain relatively smallproportions of functional groups and have relatively low molecularweight, but even these compounds do not always provide compositions ofadequate stability on storage. It has also been observed thatembrittlement of the film takes place on ageing.

Various methods have been proposed for solving the problems caused bythe high reactivity of aluminum driers. One method is to provide thecomposition as two packs so that the aluminum compound is kept separatefrom the resin until the coating composition is required for use.However, this is an inconvenient solution, and the coating composition,once mixed, must be used without delay. Another method is to dilute thecomposition containing the aluminum compound and the resin with solventuntil it has an acceptable viscosity for application. This is, however,inconvenient and wasteful of solvent, and produces variable results.

It has also been proposed to reduce the acid value of resins which,because of their acid content, tend to react rapidly with aluminumcompounds, by esterifying the free carboxyl groups by reaction with anoxirane compound, e.g. ethylene oxide, propylene oxide, epichlorohydrin,methyl glycidyl ether, phenyl glycidyl ether, glycidyl ethyl hexoate,glycidyl versatate, glycidyl hydroxide and epoxidized fatty ester.However, this does not sufficiently reduce the reactivity of the resinsand this additional reaction may undesirably affect the performance ofthe coating composition.

European Patent Specifications 0148636A and 01048637A propose to producestable compositions in which the aluminum compound is stabilized byaddition of a volatile base and water. The resulting systems are statedto be more storage stable. The presence of water is believed to inhibitreaction between alkoxide groups attached to aluminum and hydroxylgroups present in the film-forming resin. The volatile base neutralizesfree carboxyl groups present in the resin and thus prevents them fromreacting with alkoxide groups in the aluminum compound during storage.When the coating composition is used, the volatile base evaporates andallows the carboxyl groups thus released to interact with the aluminumcompound. This allows crosslinking to take place and acceptable throughdrying of the coating to be obtained. The volatile base used should havean acceptable odor and toxicity, and it is stated thatdimethylaminoethanol is preferred. However, even dimethylaminoethanolhas an odor which is unacceptable in enclosed areas, and thecompositions are thus not acceptable for interior decorating. Moreover,in practice, not all the amine evaporates and any amine remaining in thedried coating is liable to cause yellowing.

The present invention provides a novel type of aluminum complex whichcan be incorporated into coating compositions, especially compositionsof high solids content, to act as driers which improve, moreparticularly, the through drying of the coating. These new aluminumcomplexes have a reduced tendency to react with the resin in the coatingcomposition during storage. Their use involves considerable cost savingsas compared with the use of drier systems based on zirconium orneodymium. They impart little or no odor and do not cause yellowing incoatings containing them. The level of drying of the coatings obtainedis satisfactory both on the surface and through the coating, and thefilms do not tend to become brittle with age.

The aluminum complexes of the present invention are formed by reactionof a volatile ketoxime or aldoxime with an aluminum product obtained byreaction of (i) an aluminum alcoholate or phenolate with (ii) anenolizable β-diketo compound and/or a carboxylic acid and (iii)optionally water. The proportion of the volatile ketoxime or aldoximeused is preferably calculated to be at least sufficient to complex allthe unoccupied aluminum coordination sites in the aluminum product, butlower levels do show some benefits insofar as they reduce the activityof the aluminum product. The inclusion of the volatile complexing agenteffectively prevents free coordination sites on the aluminum compoundsfrom reacting with functional groups present in the coating resin. Whenthe composition is applied, the volatile ketoxime or aldoxime evaporatesand the aluminum is then able to react with the functional groups in theresin and promote through drying of the coating.

The volatile ketoxime or aldoxime used in forming the complexes of theinvention is preferably a linear, branched or cyclic ketoxime oraldoxime containing 2 to 6 carbon atoms, e.g. butyraldehyde oxime andcyclohexanone oxime, but methylethylketoxime is preferred. This compoundis known for use in paint formulations as an anti-skinning agent orstabilizing agent. For this purpose it is used in a proportion of 0.1 to0.4% by weight of the coating, and it has no reported effect on theperformance of the paint. It will be appreciated that the purpose ofsuch oximes when used in the present invention is completely different.As used herein, the oxime effectively deactivates the aluminum complexduring storage of the coating composition. When the latter is used, theoxime evaporates and the aluminum compound is reactivated. Theproportion of oxime used in the coating compositions produced inaccordance with the present invention is significantly more than theproportion heretofore used in coating compositions where it is added tothe composition as a whole and not specifically to any aluminum drierwhich may be present. It will be appreciated in this connection that,for the purpose of the present invention, sufficient of the oxime shouldbe present in the aluminum complex to complex all the aluminumcoordination sites which are present. If such sites are allowed toremain, the danger of the coating composition gelling on storageremains.

It is a further advantage of the complexes of the present invention thatthey have no unacceptable odor.

Surprisingly, it has been found that in some preferred embodiments ofthe present invention a high solids coating composition can be obtainedwith improved sag and drip resistance. It is believed that when acoating composition in accordance with the present invention is appliedand the solvent and oxime evaporate, the aluminum then reacts rapidlywith the functional groups present in the alkyd resin and atmosphericmoisture providing cross-linking and producing a pseudoplastic coating.The rheology of the coating is possibly similar to that produced byorganic aluminum compounds in printing inks where they are used toimpart pseudoplasticity so as to increase dot sharpness in printedstock. This introduction of pseudoplasticity to the coating after thecoating composition has been applied has the advantage that additivesmay still be included in the composition in order to make it thixotropicfor optimum application properties. The composition may then be appliedsatisfactorily to a vertical substrate with no viscous drag, and thepseudoplastic condition which arises after evaporation of the solventand oxime then reduces or eliminates sagging and dripping.

The new aluminum complexes may be used in coating compositions ataluminum levels rather lower than those which have previously been used.In known aluminum containing compositions, the proportion of aluminum istypically 0.5 to 2% by weight of the binder. At higher aluminum contentswithin this range embrittlement of the dried coating on ageing is likelyto occur, probably caused by continued cross-linking of the aluminumwith the resin. When the aluminum complexes of the present invention areused, the proportion of aluminum is usually in the range 0.05 to 0.2%,typically about 0.1%, based on the binder content. This reduces thepossibility of continued cross-linking with time and coatings producedusing the new aluminum complexes have not been observed to becomebrittle with age.

In some cases, coating compositions formulated with the new aluminumcomplexes have been found to have a reduced rate of surface drying. Toovercome this, more cobalt and lithium can be incorporated into thecomposition. The extra cost involved in this is not however significantand is less than would be involved in using a zirconium or neodymiumdrier.

The aluminum products with which the ketoxime or aldoxime is reacted toproduce the aluminum complexes of the invention are of two differentkinds depending on whether water is, or is not, used in making theproduct.

When water is used, the aluminum products are essentially as describedin European specification 0018780. They are made by reacting together analuminum alcoholate or phenolate, an enolizable β-diketo compound and/ora carboxylic acid, and water. According to the said Europeanspecification, these products may be represented by the formula:##STR1## wherein --O-- is an oxygen atom bridging two aluminum atoms;--OR is an alkoxy group where R is an optionally substituted alkyl groupcontaining from 1 to 4 carbon atoms or an alkoxyalkyl group containing 4to 6 carbon atoms; --X is a substituent derived by elimination of ahydrogen atom from an enolate or a mixture of substituents comprising atleast one substituent derived by elimination of a hydrogen atom from anenolate and one or more substituents derived by elimination of ahydrogen atom from an alcohol containing more than 4 carbon atoms, aphenol, a carboxylic acid, a mono-ester of a dicarboxylic acid or adi-ester of a tri-carboxylic acid or a hydroperoxy compound; p+q areindependently numbers greater than 0 with the proviso that p+q is lessthan 3; r is a number represented by the relationship ##EQU1## n is anumber of 2 or more.

For the purposes of the present invention, this formula is convenientlyrewritten as the average formula ##STR2## where X is a substituentderived from the enol form of an enolizable β-diketo compound by removalof a hydrogen atom or a carboxylate residue or a mixture of both, R isthe residue of an alcohol or phenol of formula R--OH, each of p and q isgreater than 0 and less than 2 such that (p+q)=2, p' is greater than 0up to 1 and q' is from 0 to less than 1 such that (p'+q')=1, and n is 0or more. Preferably X is an ethylacetoacetate residue and R=isopropyl orX is an octylacetoacetate residue and R=isobutyl.

These products may be made by the reaction together of an aluminumalcoholate or phenolate of formula Al(OR)₃ with an enolizable β-diketocompound and/or a carboxylic acid, and water. An appropriate solvent,more particularly an alcohol or phenol of formula ROH, may be present.Preferably an aluminum alcoholate derived from an alcohol of 1 to 4carbon atoms or an alkoxy alcohol of 4 to 6 carbon atoms is used.Preferred such alcohols are isopropanol, 2-butanol and ethoxyethanol.

The β-diketo compound is preferably an ethyl or higher ester ofacetoacetic acid, e.g. ethyl acetoacetate, acetylacetone or otherβ-diketone, diethyl malonate, or another malonic acid ester.

The carboxylic acid may be any saturated or unsaturated aliphatic orcycloaliphatic acid or aromatic acid of up to 25, preferably 6 to 25,carbon atoms. Suitable such acids include neodecanoic acid, soya oilfatty acid, erucic acid, linoleic acid, oleic acid, benzoic acid and2-ethyl-hexanoic acid.

Reference may be made to the aforesaid European specification 0018780for a description how these aluminum-containing products are made.

Alternatively, if the product is made without inclusion of water in thereaction mixture, the aluminum-containing products may be represented bythe average formula:

    Al(OR).sub.q (W).sub.n (X).sub.p

where R is the residue of an alcohol or phenol of formula R--OH, W issubstituent derived from an enolizable β-diketo compound by removal of ahydrogen atom, X is a carboxylate residue, n, q and p are each 0 to 3such that (q+n+p)=3. In a preferred example W is an acetylacetonateresidue q=0, X is a soya oil fatty acid residue, n=0.2, and p=2.8. Alsopreferred are: W=stearoyl benzoyl methane residue, n=3, and p=q=0;W=octyl acetoacetate residue, n=3, and q=p=0; W=acetylacetone residue,X=erucic acid residue, n=0.2, p=2.8, and q=0; and R=isobutyl, W=ethylacetoacetate residue, q=2, n=1 and p=0.

The aluminum alcoholate or phenolate, the β-diketo compound, and thecarboxylic acid used in making products of this formula may be the sameas those used in making the products formed in the presence of water.

Whichever type of aluminum-containing product is used, the proportion ofvolatile ketoxime or aldoxime complexed with the aluminum should be upto 3 molecules per aluminum atom. Additional oxime can be used ifrequired, and the excess then acts as a diluent and improves thestability of the complex.

The following examples describe the preparation of thealuminum-containing products.

EXAMPLE 1

    ______________________________________                                        Aluminum tri-isopropoxide                                                                             102 g                                                 Propan-2-ol(l)           25                                                   Acetyl acetone           25                                                   Soya oil fatty acid     337.5                                                 Propan-2-ol(2)           25                                                   Propan-2-ol(3)           25                                                   Methylethylketoxime     261.4                                                 ______________________________________                                    

The aluminum tri-isopropoxide and propan-2-ol(1) were charged to a flaskfitted with a stirrer, thermometer, nitrogen purge and a condenser forrefluxing and distillation. Stirring was commenced and the solution washeated to 50° C. The acetylacetone was then added via a dropping funnel(over 5 mins.). The exothermic reaction caused the temperature to riseto 58° C. The mixture was further heated to 80° C. A solution of soyaoil fatty acid in propan-2-ol(2) was added by a dropping funnel over aperiod of 30 minutes, maintaining the temperature of the reactionmixture at 80° C.

The dropping funnel was flushed with propan-2-ol(3) and the washingstransferred to the flask. The mixture was heated to reflux and held forone hour. The apparatus was set up for distillation and heated.Distillation commenced at 92° C. and was continued at atmosphericpressure until 137° C. was reached. The flask was then cooled to 105° C.and vacuum was applied with heating until distillation ceased at 110° C.The product was cooled to 70° C. and the methylethylketoxime was addedduring a 5 minute period via a dropping funnel.

EXAMPLE 2

Example 1 was repeated but using 391.2 g of the soya oil fatty acid and10 g of acetylacetone.

EXAMPLE 3

Example 1 was repeated using 285 g of cekanoic acid (in place of thesoya oil fatty acid) and no acetylacetone.

EXAMPLE 4

Example 1 was repeated using 395.5 g of oleic acid (in place of the soyaoil fatty acid) and 10 g of acetylacetone.

EXAMPLE 5

Example 1 was repeated using 216 g of 2-ethyl-hexanoic acid (in place ofthe soya oil fatty acid) and no acetylacetone.

EXAMPLE 6

Example 1 was repeated using 512.2 g of erucic acid (in place of thesoya oil fatty acid) and 10 g of acetylacetone.

EXAMPLE 7

    ______________________________________                                        Aluminum Triisopropoxide:                                                                             409 g                                                 Ethylacetoacetate:      260 g                                                 Propan-2-ol:            95.5 g                                                Water:                  40.3 g                                                Butan-2-ol:             38.5 g                                                Methylethylketoxime:    522.7 g                                               ______________________________________                                    

The aluminum tri-isopropoxide was charged to a flask fitted with astirrer, thermometer, nitrogen purge and a condenser for refluxing anddistillation. Stirring was commenced and the aluminum tri-isopropoxidewas heated to 90° C. The ethylacetoacetate was then added (over 2.5hours) maintaining the temperature of the mixture at 90° C. Oncompletion of addition, the mixture was held at 90° C. for 30 minutes.The mixture was then distilled until a vessel temperature of 150° C. wasattained. The mixture was held at 150° C. for 30 minutes and then cooledto 85° C.

A mixture of the water and the propan-2-ol was then added (over 1.5hours), the exothermic reaction being sufficient to maintain refluxwithout additional heating. On completion of addition, the reactionmixture was refluxed for 30 minutes. The mixture was then distilleduntil a vessel temperature of 150° C. was attained. The mixture was thenheld at 150° C. for 30 minutes.

The butan-2-ol was then added (over 30 minutes). During the addition,the vessel temperature falls to 110°-115° C. On completion of addition,the reaction mixture was held at 110°-115° C. for 30 minutes.

The mixture was then distilled until a vessel temperature of 150° C. wasattained. A nitrogen bleed was used to help distillation. Vacuum (29in.Hg) was then applied to the vessel and the reaction mixture distilledunder vacuum at 150° C. for 30 minutes. The vessel was then returned toatmospheric pressure and the reaction mixture was cooled to 125° C. 50%of the methylethylketoxime was added which cooled the mixture to 75°-80°C. The mixture was held at 75°-80° C. for 30 minutes. The remainingmethylethylketoxime was then added and the mixture cooled to 30°-40° C.

The aluminum complexes prepared as described as above were compared withstandard driers in paint formulations based on the following high solidsalkyd resins.

    ______________________________________                                        Cargill 57-5766                                                               Type:               Long oil alkyd                                            Acid value (mg KOH/G)                                                                             10.0                                                      Non volatile content:                                                                             90.0%                                                     Viscosity (Gardener):                                                                             Z1-Z3                                                     Solvents:           mineral spirits/xylene                                    Beckosol 10-539                                                               Type:               Pure drying Alkyd                                         Acid value (mg KOH/g):                                                                            10.0                                                      Non volatile content:                                                                             90.0%                                                     Viscosity (Gardener):                                                                             Z1-Z3                                                     Solvent:            Mineral spirits                                           ______________________________________                                    

High solids, high gloss paints were prepared from these alkyds accordingto the following formulations:

    ______________________________________                                        Mill base                                                                     High solids alkyd        935.0 g                                              Titanium dioxide (RCL-535)                                                                            1706.0                                                White spirit             212.0                                                Let down                                                                      High solids alkyd       1395,0 g                                              White spirit             482.8                                                ______________________________________                                    

The paints were prepared on a high speed disperser to produce paintswith the following properties:

    ______________________________________                                        Hegmann Value    8.0                                                          Pigment:Binder ratio                                                                           0.8:1.0                                                      Viscosity (25c) (poises)                                                                       5.0 (Cargill)/7.0 (Beckosol)                                 Binder Content   44.3%                                                        Non volatile content                                                                           84.2%                                                        ______________________________________                                    

In the Cargill-based paint a standard drier system incorporating ahigher than normal level of zirconium was used. This standard systemcontained 0.08% cobalt, 0.2% calcium, 0.2% zirconium, based on weight ofbinder, and 0.2% by weight of the paint of anti-skinning agent, viz.methylethylketoxime. This standard system was tested and comparedagainst unstabilized and stabilized aluminum complexes which were usedat 0.08% cobalt and 0.1% aluminum based on weight of binder.

In the Beckosol-based paint, a standard drier system with a higher levelof zirconium and lithium was used, as recommended by Reichhold (theManufacturers of Beckosol) to improve the surface and through drying.The standard Beckosol system contained 0.06% cobalt, 0.03% lithium, 0.2%calcium and 0.2% zirconium by weight of binder and 0.2% by weight ofpaint of anti-skinning agent, i.e. methylethylketoxime. This wascompared with systems containing stabilized and unstabilized aluminumwhich were used at 0.08% cobalt, 0.03% lithium and 0.1% aluminum byweight of binder. In this case the higher level of cobalt in conjunctionwith lithium was required to overcome the slight reduction in surfacedrying that occurred with the stabilized aluminum complexes.

The storage stability of both paint systems was assessed initially andafter 1 month's storage at 50° C. The results showed that the stabilizedaluminum complexes provided acceptable stability in the Cargill andBeckosol paints. The stability results are shown below.

    ______________________________________                                                           Low Shear Viscosity                                                           (poises/25° C.)                                                              4 weeks at                                                              Initial                                                                             50° C.                                        ______________________________________                                        Cargill paints                                                                Standard             5       8.5                                              Stabilized aluminum carboxylate                                                                    5       10                                               complex of Example 2                                                          Stabilized polyoxo-aluminum                                                                        5       12                                               complex of Example 7                                                          Unstabilized aluminum                                                                              8       gelled                                           compound Alusec 588*                                                          Beckosol paints                                                               Standard             14.5    21                                               Stabilized aluminum carboxylate                                                                    12.0    12.5                                             complex of Example 2                                                          Stabilized polyoxo-aluminum                                                                        13.5    15.0                                             complex of Example 7                                                          Unstabilized aluminum                                                                              19.0    gelled                                           compound Alusec 588*                                                          ______________________________________                                         *Alusec 588 is a commercially available aluminum containing drier sold by     RhonePoulenc Chemicals Ltd. containing 7.1% aluminum.                    

Beck Koller and Ballotini drying tests were carried out at 25° C. and65% relative humidity at a film thicknesses of 75 microns. The Ballotinithrough drying time is an in-house developed test where a 200 micron wetpaint film is allowed to surface dry. The paint film is then peeled backby fingernail and the films were classified "Ballotini through dry" whenBallotini would not stick to the surface. In this test Ballotini throughdrying times were carried out at 25° C. and 65% relative humidity. Ingeneral the aluminum containing systems increased the rate of throughdrying compared to the standard systems. In terms of gloss,embrittlement and yellowing resistance, there was no measurabledifference between the systems.

An example of the increased through drying performance for the Cargillsystem is given below.

    ______________________________________                                                            Beck Koller                                                                              Ballotini                                                          (Stage 4)  Through                                        Cargill Paints      HOURS      DAYS                                           ______________________________________                                        Standard            8.5        19                                             Stabilized aluminum carboxy-                                                                      3.2        13                                             late complex of Example 2                                                     Stabilized polyoxo aluminum                                                                       3.7        19                                             complex of Example 7                                                          ______________________________________                                    

Using the Cargill 57-5766 alkyd a white, medium tint base was prepared.In this system a level of 0.6% zirconium in conjunction with 0.2%"Active 8" (38 % 1,10-phenanthroline in n-butanol and 2-ethyl-hexanoicacid from RT Vanderbilt Co. Inc.) is recommended by Cargill to produceadequate through drying. The standard system used contained 0.04%cobalt, 0.6% zirconium, 0.2% Active 8 based on binder and 0.1%anti-skinning agent based on the weight of the paint. This system wascompared against the two stabilized aluminum systems using 0.04% cobaltand 0.1% aluminum for the stabilized aluminum carboxylate and 0.08% Co,0.01% lithium and 0.1% aluminum for the stabilized polyoxo-aluminumcompound.

    ______________________________________                                        Millbase                                                                      ______________________________________                                        Cargill 57-5766 (high solids alkyd from                                                                   570.0                                             Cargill Inc.)                                                                 Daniels XL1/80 (Dispersant, Daniel Products Co.)                                                          11.4                                              Maximix 6 (calcium carbonate of Cyprus Industrial                                                         153.1                                             Minerals Corp.)                                                               Minex 7 (sodium potassium aluminum silicate of                                                            357.7                                             Lindusmin Ltd.)                                                               Titanium Dioxide (RCL 535 of SCM Chemicals)                                                               777.5                                             White spirit (184 aromatics from Carless                                                                  34.2                                              Refining and Marketing Co.)                                                   Exxsol D40 (100% aliphatic from Exxon                                                                     79.8                                              Chemicals Ltd.)                                                               ______________________________________                                    

This was dispersed to Hegmann 7.0 using a high speed disperser.

    ______________________________________                                        Letdown                                                                       ______________________________________                                        Cargill 57-5766        2292.7                                                 Daniels XLI/80         4.6                                                    BYK 077 (defoamer from Byk-Chemie)                                                                   11.4                                                   White spirit           24.5                                                   Exxsol D40             57.2                                                   Solvesso 100 (100% aliphatic solvent)                                                                100.9                                                  ______________________________________                                    

The letdown was slowly added to the mill base with stirring. This paintwas then tinted with Huls blue, red, black and green tinters (HulsAmerica Inc. colortrend 888 universal machine colorants) to producestrong colors ranging from binder contents of 54 to 58%. The finalproperties of the paint were:

Pigment:binder ratio: 0.5:1.0

Binder content: 54-58% depending on colorant used.

Volatile content: In the region of 236 g per liter.

The stabilized aluminum complex systems of the present inventionproduced adequate stability in all systems and improved the storagestability in the colored systems. This is shown below for the coloredsystems.

    ______________________________________                                                     Low shear Viscosity                                                           (poises/25° C.)                                                        Initial/4 weeks at 50° C.                                              Red   Black    Green   Blue                                      ______________________________________                                        Standard       50/51   42/48    35/46 42/56                                   Stabilized aluminum                                                                          41/36   37/35    32/29 30/33                                   carboxylate of Example 2                                                      Stabilzed polyoxo-                                                                           48/45   42/38    33/37 33/37                                   aluminum of Example 7                                                         ______________________________________                                    

Beck-Koller drying times were carried out at 25° C. and 65% relativehumidity at a film thicknesses of 75 microns. The Ballotini results weremeasured under laboratory conditions of approximately 16° C. The surfaceBallotini results were carried out on 75 micron films, whilst thethrough Ballotini results were assessed at 200 microns. In general, thethrough and surface drying as well as the loss of dry on ageing of thealuminum systems were equivalent to the standard system, which contained0.6% zirconium and 0.2% "Active 8". However, the surface drying of thepolyoxo-aluminum complex system was improved. This was expected becausethis system had an increased cobalt level. In these systems there was nomajor differences in terms of gloss, yellowing resistance orembrittlement.

Using the Beckosol 10-539 alkyd resin, a white gloss exterior housepaint was produced. The standard system recommended by Reichhold to drythis paint is 0.042% cobalt, 0.104% neodymium (Neochem 250 of MooneyChemicals), 0.024% Vanadium and 0.012% potassium (Cur-RX of MooneyChemicals), and 0.231% of 2,2-dipyridyl solution (Drymax of HulsAmerican Inc.). This was compared against 0.08% cobalt, 0.1% Aluminumand 0.03% lithium using both the stabilized aluminum complexes.

    ______________________________________                                        Mill base                                                                     ______________________________________                                        Beckosol 10-539 (High solids alkyd of                                                                     1240 g                                            Reichold Chemicals Inc.)                                                      Daniels XLI/80 (Dispersant of Daniel Products Co.)                                                         39.9                                             Titanium dioxide white pigment (RCL 535 of                                                                1198.3                                            SCM Chemicals)                                                                Cetacarb OG (calcium carbonate of                                                                          530.9                                            Croxton and Garry Ltd.)                                                       Snowcal 10ML (calcium carbonate of                                                                         267.2                                            Croxton and Garry Ltd.)                                                       Nopcocide N96 (Biocide of Henkel)                                                                          29.9                                             ______________________________________                                    

This was dispersed using a high speed disperser to Hegmann 6.

    ______________________________________                                        Let Down                                                                      Bentone pregel          490.4                                                 Beckosol 10-539         644.8                                                 40 poise stand oil brushing aid                                                                       299.8                                                 (Samuel Banners)                                                              Exxsol D40              268.2                                                 White spirit            16.9                                                  Bentons Pregel                                                                Exxsol D40              429.2                                                 White spirit            27.0                                                  Bentone 38 (Steetley Minerals)                                                                        73.3                                                  Mix well at low speed and add:                                                Anti-terra U (Byk-Chemie)                                                                             5.4                                                   Propylene Carbonate (Fluka Chemicals)                                                                 1.39                                                  Mix at high speed until gelled.                                               ______________________________________                                    

This paint system was tinted with red, black, yellow and blue tinters toproduce paints which had binder contents varying from 31 to 34%. Thepaints had the following properties:

Pigment:binder ratio: 1.1

Binder content: 31-34% depending on the colorant used.

Volatile content: In the region of 248 g per liter.

All the paints produced acceptable visco-stability and the rate ofsurface drying was quicker for the aluminum-containing systems than itwas for the standard system. The increase in surface dry is probably dueto the increased cobalt levels in these systems. In terms of throughdrying, equivalent results for the standard and aluminum-containingsystems were obtained.

Surprisingly when the loss of dry on ageing (1 month at 50° C. at 76microns) was tested for the standard neodymium systems, it was foundthat all the tinted paints were still wet to touch after 48 hours dryingat 25° C./65% relative humidity, whereas the stabilized aluminum systemswere touch dry in less than 24 hours. In the white systems the neodymiumsystem performed to the same extent as the stabilized aluminum systemsproducing surface drying times of 5 hours and through drying times of 20hours. In all of the systems there was no major differences in terms ofgloss, yellowing resistance or embrittlement.

The invention accordingly includes within its scope compositions,especially paint compositions and more particularly those having a highsolids content preferably based on a synthetic resin, and especially anair drying alkyd resin comprising, as a cross-linker (drier) for thebinder, an aluminum complex containing an oxime as described above.

We claim:
 1. A coating composition comprising an air-drying alkyd resinbinder and a cross-linking agent consisting of an aluminum complex, saidaluminum complex formed by a process comprising the steps of:(a) formingan aluminum product having aluminum coordination sites by reacting (i)an aluminum alcoholate or phenolate with (ii) an enolizable β-diketocompound or a carboxylic acid; and (b) forming the aluminum complex byreacting said aluminum product with a volatile ketoxime or aldoximecompound, the proportion of said volatile ketoxime or aldoxime compoundbeing sufficient to complex all of the aluminum coordination sites insaid aluminum product.
 2. An aluminum complex formed by a processcomprising the steps of:(a) forming an aluminum product having aluminumcoordination sites by reacting (i) an aluminum alcoholate or phenolatewith (ii) an enolizable β-diketo compound or a carboxylic acid; and (b)forming the aluminum complex by reacting said aluminum product with avolatile ketoxime or aldoxime compound, the proportion of said volatileketoxime or aldoxime compound being sufficient to complex all of thealuminum coordination sites in said aluminum product.
 3. An aluminumcomplex according to claim 2, wherein said reaction in step (a) isconducted in the presence of water.
 4. An aluminum complex according toclaim 2, wherein said volatile ketoxime or aldoxime compound has from 2to 6 carbon atoms.
 5. An aluminum complex according to claim 4, whereinsaid volatile ketoxime or aldoxime compound is methlethylketoxime.